Effects of dietary n−3 polyunsaturated fatty acids on T-Cell membrane composition and function

Dietary n−3 PUFA have been shown to attenuate T-cell-mediated inflammation, in part, by suppressing T-cell activation and proliferation. n−3 PUFA have also been shown to promote apoptosis, another important mechanism for the prevention of chronic inflammation by maintaining T-cell homeostasis through the contraction of populations of activated T cells. Recent studies have specifically examined Fas death receptor-mediated activation-induced cell death (AICD), since it is the form of apoptosis associated with peripheral T-cell deletion involved in immunological tolerance and T-cell homeostasis. Data from our laboratory indicate that n−3 PUFA promote AICD in T helper 1 polarized cells, which are the mediators of chronic inflammation. Since Fas and components of the deathinducing signaling complex are recruited to plasma membrane microdomains (rafts), the effect of dietary n−3 PUFA on raft composition and resident protein localization has been the focus of recent investigations. Indeed, there is now compelling evidence that dietary n−3 PUFA are capable of modifying the composition of T-cell membrane microdomains (rafts). Because the lipids found in membrane microdomains actively participate in signal transduction pathways, these results support the hypothesis that dietary n−3 PUFA influence signaling complexes and modulate T-cell cytokinetics in vivo by altering T-cell raft composition.     

Effects of dietary supplementation of saturated fatty acids and of n−6 or n−3 polyunsaturated fatty acids on plasma and red blood cell membrane phospholipids and deformability in weanling guinea pigs

The fatty acid composition of plasma cholesteryl esters, plasma phospholipids, red blood cell (RBC) membrane phosphatidylcholine (corresponding to the outer membrane leaflet), and phosphatidylethanolamine (corresponding to the inner membrane leaflet) was investigated in weanling guinea pigs fed with diets of cacao (saturated fatty acids), sunflower oil [n−6 polyunsaturated fatty acids (PUFA)] or fish oil (n−3 PUFA) for 20 wk. RBC deformation was measured by means of a cell-transit analyzer (filtration) and a cone-plate rheoscope. The contents of saturated fatty acids in plasma phospholipids and RBC membrane leaflets were similar in all three groups. Diets with sunflower oil resulted in a high content of linoleic acid in plasma cholesteryl esters and in the outer leaflet of RBC membranes. Fatty acids of fish oil were mainly incorporated in plasma phospholipids and in the inner leaflet of RBC membranes. The arachidonic acid content was high in all groups in the plasma phospholipids and in the inner leaflet. The n−6 and n−3 PUFA were mainly incorporated in the inner leaflet. In all groups the polyunsaturated/saturated fatty acid ratio and the total PUFA content were similar in the inner RBC membrane. The RBC filtration times and the RBC deformation indices were not affected by the dietary treatment.     

n−3 polyunsaturated fatty acids and coronary thrombosis

Studies of Greenland Eskimos showed that a very high intake of marine n?3 fatty acids markedly inhibited platelet reactivity and suggested that intake of these fatty acids might prevent coronary thrombosis. Later studies with lower, more practical doses of n?3 fatty acids also have shown a platelet inhibitory effect of n?3 fatty acids, albeit fairly marginal. Furthermore, n?3 fatty acids have little effect on measures of blood coagulability and may slightly decrease fibrinolysis. In animal models, n?3 fatty acids often have been shown to inhibit thrombosis, but again the doses have tended to be very high. Finally, there has been little effect of (low-dose) n?3 fatty acids in clinical trials in humans on the incidence of myocardial infarction. Overall, there is little evidence for a major antithrombotic effect of practical doses of n?3 fatty acids on coronary thrombosis. This does not exclude a beneficial effect of n?3 fatty acids on coronary heart disease as suggested from clinical trials, but the major effect may be antiarrhythmic rather than antithrombotic.     

Effect of species and genotype on the efficiency of enrichment of poultry meat with n−3 polyunsaturated fatty acids

The effect of poultry species (broiler or turkey) and genotype (Wrolstad or BUT T8 turkeys and Ross 308 or Cobb 500 broilers) on the efficiency with which dietary long-chain n−3 PUFA were incorporated into poultry meat was determined. Broilers and turkeys of both genotypes were fed one of six diets varying in FA composition (two replicates per genotype x diet interaction). Diets contained 50 g/kg added oil, which was either blended vegetable oil (control), orpartially replaced with linseed oil (20 or 40 g/kg diet), fish oil (20 or 40 g/kg diet), or a mixture of the two (20 g linseed oil and 20 g fish oil/kg diet). Feeds and samples of skinless breast and thigh meat were analyzed for FA. Worlstad dark meat was slightly more responsive than BUT T8 (P=0.046) to increased dietary 18∶3 concentrations (slopes of 0.570 and 0.465, respectively). The Ross 308 was also slightly more responsive than the Cobb 500 (P=0.002) in this parameter (slopes of 0.557 and 0.449). There were no other significant differences between the genotypes. There was some evidence (based on the estimates of the slopes and their associated standard errors) that white turkey meat was more responsive than white chicken meat to 20∶5 (slopes of 0.504 and 0.289 for turkeys and broilers, respectively). There was no relationship between dietary 18∶3 n−3 content and meat 20∶5 and 22∶6 contents. If birds do convert 18∶3 to higher FA, these acids are not then deposited in the edible tissues.     

Influence of dietary supplementation with long-chain n−3 or n−6 polyunsaturated fatty acids on blood inflammatory cell populations and functions and on plasma soluble adhesion molecules in healthy adults

Greatly increasing the amounts of flaxseed oil [rich in α-linolenic acid (ALNA)] or fish oil (FO); [rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] in the diet can decrease inflammatory cell functions and so might impair host defense. The objective of this study was to determine the effect of dietary supplementation with moderate levels of ALNA, γ-linolenic acid (GLA), arachidonic acid (ARA), DHA, or FO on inflammatory cell numbers and functions and on circulating levels of soluble adhesion molecules. Healthy subjects aged 55 to 75 yr consumed nine capsules per day for 12 wk. The capsules contained placebo oil (an 80∶20 mix of palm and sunflowerseed oils) or blends of placebo oil with oils rich in ALNA, GLA, ARA, or DHA or FO. Subjects in these groups consumed 2 g ALNA; approximately 700 mg GLA, ARA, or DHA; or 1 g EPA plus DHA (720 mg EPA+280 mg DHA) daily from the capsules. Total fat intake from the capsules was 4 g per day. None of the treatments affected inflammatory cell numbers in the bloodstream; neutrophil and monocyte phagocytosis or respiratory burst in response to E. coli; production of tumor necrosis factor-α, interleukin-1β, and interleukin-6 in response to bacterial lipopolysaccharide; or plasma concentrations of soluble intercellular adhesion molecule-1. In contrast, the ALNA and FO treatments decreased the plasma concentrations of soluble vascular cell adhesion molecule-1 (16 and 28% decrease, respectively) and soluble E-selectin (23 and 17% decrease, respectively). It is concluded that, in contrast to previous reports using higher amounts of these fatty acids, a moderate increase in consumption of long-chain n−6 or n−3 polyunsaturated fatty acids does not significantly affect inflammatory cell numbers or neutrophil and monocyte responses in humans and so would not be expected to cause immune impairment. Furthermore, we conclude that moderate levels of ALNA and FO, which could be incorporated into the diet, can decrease some markers of endothelial activation and that this mechanism of action may contribute to the reported health benefits of n−3 fatty acids.     

Induction of apoptosis and apoptotic mediators in balb/C splenic lymphocytes by dietary n−3 and n−6 fatty acids

The present study was designed to investigate the effect of diatery n−6 and n−3 polyunsaturated fatty acids (PUFA) on anti-CD3 and anti-Fas antibody-induced apoptosis and its mediators in mouse spleen cells. Nutritionally adequate semipurified diets containing either 5% w/w corn oil (n−6 PUFA) or fish oil (n−3 PUFA) were fed to weanling female Balb/C mice, and 24 wk later mice were sacrificed. In n−3 PUFA-fed mice, serum and splenocyte lipid peroxides were increased by 20 and 28.3% respectively, compared to n−6 PUFA-fed mice. Further, serum vitamin F levels were decreased by 50% in the n−3 PUFA-fed group, whereas higher anti0Fas- and anti-CD3-induced apoptosis (65 and 66%) and necrosis (17 and 25%), compared to the n−6 PUFA-fed group, were found when measured with Annexin V and propidium iodide staining, respectively. In addition, decreased Bcl-2 and increased Fas-ligand (Fas-L) also were observed in the n−3 PUFA-fed group compared to the n−6 PUFA-fed group. No difference in the ratio of splenocyte subsets nor their Fas expression was observed between the n−3 PUFA-fed and n−6 PUFA-fed groups, whereas decreased proliferation of splenocytes was found in n−3 PUFA-fed mice compared to n−6 PUFA-fed mice. In conclusion, our results indicate that dietary n−3 PUFA induces higher apoptosis by increasing the generation of lipid peroxides and elevating Fas-L expression along with decreasing Bcl-2 expression. A reduced proliferative response of immune cells also was observed in n−3 PUFA-fed mice.     

Modification of milk formula to enhance accretion of long-chain n−6 and n−3 polyunsaturated fatty acids in artificially reared infant rats

Artificially reared infant rats were used to determine the effects of long-chain polyunsaturated fatty acid (LCP-UFA) supplementation on blood and tissue concentrations of arachidonic acid (AA) and docosahexaenoic acid (DHA). Beginning at 7 d of age, infant rats were fed for 10 d with rat milk formulas supplemented with AA at 0,0.5 and 1.0%, or supplemented with DHA at 0,0.5 and 1.0% of total fatty acid. The supplementation of AA increased accretion of the fatty acid in tissue and blood phospholipids with a maximum increase of 9% in brain, 15% in liver, 25% in erythrocytes, and 43% in plasma above the values of unsupplemented infant rats. Rat milk formula containing 1.0% of AA had no added benefits over that containing 0.5% of AA. The supplementation of DHA increased phospholipid DHA by a maximum of 24% in brain, 87% in liver, 54% in erythrocytes, and 360% in plasma above the unsupplemented control. The increase in tissue and blood DHA was concentration-dependent on formula fatty acid. Brain phosphatidylcholine and phosphatidylethanolamine were similarly enriched with AA and DHA by supplementation of the corresponding fatty acids. In general the observed increase of AA was accompanied by a decrease in 16:0, 18:1n−9, and/or 18:2n−6, whereas the increased DHA was associated with a reduction of 18:1n−9, 18:2n−6, and/or 20:4n−6. Clearly, infant rats were more responsive to DHA than AA supplementation, suggesting a great potential of dietary manipulation to alter tissue DHA concentrations. However, the supplementation of DHA significantly decreased tissue and blood AA/DHA ratios (wt%/wt%), whereas there was little or no change in the ratio by AA supplementation. Although the physiological implications of the levels of AA and DHA, and AA/DHA ratios achieved under the present experimental conditions are not readily known, the findings suggest that artificial rearing could provide a suitable model to investigate LCPUFA requirements using various sources of AA and DHA in rats.     

Effect of n−3 polyunsaturated fatty acid supplementation on lipid peroxidation of rat organs

The present study was undertaken in order to reexamine the effect of n−3 polyunsaturated fatty acid (PUFA)-rich diet supplementation on lipid peroxidation and vitamin E status of rat organs. Male Wistar rats were fed a diet containing safflower or fish oil at 50 g/kg diet and an equal amount of vitamin E at 59 mg/kg diet (1.18 g/kg oil; and 1.5 g/kg PUFA in safflower oil diet, and 4.3 g/kg PUFA in fish oil diet) for 6 wk. Fatty acid composition of total lipids of brain, liver, heart, and lung of rats fed fish oil was rich in n−3 PUFA, whereas that of each organ of rats fed safflower oil was rich in n−6 PUFA. The vitamin E levels in liver, stomach, and testis of the fish oil diet group were slightly lower than those of the safflower oil diet group, but the levels in brain, heart, lung, kidney, and spleen were not different between the two diet groups. The levels of phospholipid hydroperoxides were determined by the high-performance liquid chromatography-chemiluminescence method and the levels of thiobarbituric acid-reactive substances (TBARS) were determined at pH 3.5 in the presence of butylated hydroxytoluene with or without EDTA. Levels of phospholipid hydroperoxides and TBARS in the brain, liver, heart, lung, kidney, spleen, stomach and testis of the fish oil diet group were similar to those of the safflower oil diet group. The results indicate that high fish oil intake does not induce increased levels of phospholipid hydroperoxides and TBARS in rat organs.     

Effects of aging and dietary n−3 fatty acids on rat brain phospholipids: Focus on plasmalogens

The aging brain undergoes modifications in the lipid composition of cell membranes and especially in plasmalogens. These phospholipids represent between one-half and twothirds of the ethanolamine phospholipids in the brain. They are known to facilitate membrane fusion and act as endogenous antioxidants. During normal aging and in some pathological conditions, plasmalogen and DHA levels fall. In this context, we aimed to evaluate the influence of n−3 FA intake on plasmalogens in the brain during aging. Littermates from two generations of n−3-deficient rats were fed an n−3-deficient diet or an equilibrated diet containing either α-linolenic acid alone (α-LNA) or with two doses of DHA (0.3 or 0.6% w/w). After weaning, 9 mon of diet, or 21 mon of diet, plasmalogen levels were assessed, and the sn-2 substitutions of plasmenylethanolamines were analyzed in the cortex, striatum, and hippocampus. Our results showed that plasmalogen contents were not influenced by the diet. Plasmalogen levels were significantly decreased in aged rats compared with adults, whereas DHA levels increased in the hippocampus and remained stable in the cortex and striatum. DHA levels were significantly and similarly increased in total phospholipids and especially in plasmenylethanolamines after 9 mon of diet containing α-LNA alone or combined with DHA. This study showed that each structure sustained specific age-induced modifications. Dietary n−3 FA may not oppose the physiological decrease in brain plasmalogen levels during aging. Moreover, α-LNA appears to be equally as potent as preformed DHA at replacing DHA in the brain of our rat model.     

n−3 fatty acids and revascularization procedures

Largely initiated by studies among Greenland Eskimos in the early 1970s, great attention has been given to the possible effects of the very long chain n?3 polyunsaturated fatty acids (PUFA) in a variety of cardiovascular disease states. A series of possibly positive effects on pathogenetic mechanisms in cardiovascular disease has evolved from laboratory studies in cell cultures and animals as well as in humans, focusing mainly on eicosanoid metabolism with reduced activities of platelets and leucocytes, reduced plasma triglycerides and, antiarrhythmic effects in the myocardium. A rationale for a positive effect of very long chain n?3 PUFA in the secondary prophylaxis after revascularization procedures obviously also exists. The positive clinical effects based on prospectively randomized trials are summarized as follows. After coronary artery bypass grafting (CABG), the SHOT study showed statistically significant reduction in angiographic vein graft occlusion in 610 patients after 1 yr with supplementation of 3.4 g/d of highly concentrated very long chain n?3 PUFA. The reduction in occlusion rates was significantly related to the change in the n?3 PUFA concentration in serum phospholipids during the study period with the occlusion rate in the upper quartile of such changes at only ～50% of that in the lower quartile. These results were also clearly related to the presence of angina pectoris and occurrence of myocardial infarction after 1 yr. Several studies were conducted in patients after percutaneous transluminal coronary angioplasty (PTCA). By 1993, two meta-analyses indicated a positive effect on the restenosis rate, a significant problem after otherwise successful PTCA. During the late 1990s, three large prospective randomized placebo-controlled angiographic studies were conducted with very long n?3 PUFA 5.1–8.0 g/d, all with completely negative results. Today, therefore, very long chain n?3 PUFA supplementation cannot be recommended to reduce the incidence of restenosis after PTCA. All studies were performed without stenting of the coronary lesion. In the very special revascularization procedure of heart transplantation, evolving hypertension and accelerated atherosclerosis have been major clinical problems. In other studies, positive effects by supplementation with very long chain n?3 PUFA (3.4–5.7 g/d) were obtained on the surrogate end points coronary vasoreactivity to acetylcholine and hypertension, respectively. On the basis of the presently available literature from clinical studies, recommendations for supplementation with very long chain n?3 PUFA can be given to patients after venous CABG (up to 3.4 g/d), and after heart transplantation (3.4–5.7 g/d) but not to patients after traditional PTCA. In fact, data from substudies suggested the possibility that large doses (5.1 g/d) of very long chain n?3 PUFA might be contraindicated because they induce a proinflammatory state in patients under oxidative stress.     

Metabolism of n−3 and n−6 fatty acids in Atlantic salmon liver: Stimulation by essential fatty acid deficiency

Oxidation, esterification, desaturation, and elongation of [1-¹⁴C]18∶2n−6 and [1-¹⁴C]18∶3n−3 were studied using hepatocytes from Atlantic salmon (Salmo salar I.) maintained on diets deficient in n−3 and n−6 polyunsaturated fatty acids (PUFA) or supplemented with n−3 PUFA. For both dietary groups, radioactivity from 18∶3n−3 was incoporated into lipid fractions two to three times faster than from 18∶2n−6, and essential fatty acids (FFA) deficiency doubled the incorporation. Oxidation to CO₂ was very low and was independent of substrate or diet, whereas oxidation to acid-soluble products was stimulated by EFA deficiency. Products from 18∶2n−6 were mainly 18∶3n−6, 20∶3n−6, and 20∶4n−6, with minor amounts of 20∶2n−6 and 22∶5n−6. Products from 18∶3n−3 were mainly 18∶4n−3, 20∶5n−3, and 22∶6n−3, with small amounts of 20∶3n−3. The percentage of 22∶6n−3 in the polar lipid fraction of EFA-deficient hepatocytes was fourfold higher than in n−3 PUFA-supplemented cells. This correlated well with our other results obtained after abdominal injection of [1-¹⁴C]18∶3n−3 and [1-¹⁴C]18∶2n−6. In hepatocytes incubated with [4,5-³H]-22∶6n−3, 20∶5n−3 was the main product. This retrocon-version was increased by EFA deficiency, as was peroxisomal β-oxidation activity. This study shows that 18∶2n−6 and 18∶3n−3 can be elongated and desaturated in Atlantic salmon liver, and that this conversion and the activity of retroconversion of very long chain PUFA is markedly enhanced by FFA deficiency.     

The metabolism and n−6/n−3 ratio of essential fatty acids in rats: Effect of dietary arachidonic acid and a mixture of sesame lignans (sesamin and episesamin)

In this study, we examined the effect of dietary arachidonic acid (AA) and sesame lignans on the content and n-6/n-3 ratio of polyunsaturated fatty acid (PUFA) in rat liver and the concentrations of triglyceride (TG) and ketone bodies in serum. For 4 wk, rats were fed two types of dietary oils: (i) the control oil diet groups (CO and COS): soybean oil/perilla oil=5∶1, and (ii) the AA-rich oil group (AO and AOS): AA ethyl esters/palm oil/perilla oil=2∶∶1, with (COS and AOS) or without (CO and AO) 0.5% (w/w) of sesame lignans. Dietary AA and sesame lignans significantly affected hepatic PUFA metabolism. AA content and n-6/n-3 ratio in the liver were significantly increased in the AO group, despite the dietary total of n-6 PUFA being the same in all groups, while AOS diet reduced AA content and n-6/n-3 ratio to a level similar to the CO and COS groups. These results suggest that (i) dietary AA considerably affects the hepatic profile and n-6/n-3 ratio of PUFA, and (ii) dietary sesame lignans reduce AA content and n-6/n-3 ratio in the liver. In the AO group, the concentration of acetoacetate was significantly increased, but the ratio of β-hydroxybutyrate/acetoacetate was decreased. On the other hand, the AO diet increased the concentration of TG in serum by almost twofold as compared to other groups. However, the AOS diet significantly reduced serum IG level as compared to the AO group. In addition, the AOS diet signicantly increased the acetoacetate level, but reduced the β-hydroxybutyrate/acetoacetate ratio. These results suggest that dietary sesame lignans promote ketogenesis and reduce PUFA esterification into TG. This study resulted in two findings: (i) sesame lignans inhibited extreme changes of the n-6/n-3 ratio by reducing hepatic PUFA content, and (ii) the reduction of hepatic PUFA content may have occurred because of the effects of sesame lignans on PUFA degradation (oxidation) and esterification.     

Paradoxical effect of n−3-containing vegetable oils on long-chain n−3 fatty acids in rat heart

Flaxseed, echium, and canola oils contain α-linolenic acid (18∶3n−3, ALA) in a range of concentrations. To examine their effect on elevating cardiac levels of long-chain n−3 FA, diets based on these n−3-containing vegetable oils were fed to rats for 4 wk. Sunflower oil, which contains little ALA, was a comparator. Despite canola oil having the lowest ALA content of the three n−3-containing vegetable oils, it was the most potent for elevating DHA (22∶6n−3) levels in rat hearts and plasma. However, the relative potencies of the dietary oils for elevation of EPA (20∶5n−3) in heart and plasma followed the same rank order as their ALA content, i.e., flaxseed>echium>canola>sunflower oil. This paradox may be explained by lower ALA intake leading to decreased competition for Δ6 desaturase activity between ALA and the 24∶5n−3 FA precursor to DHA formation.     

Differential effect of N-ethyl maleimide on Δ6-desaturase activity in human fetal liver toward fatty acids of the n−6 and n−3 series

The effect of N-ethyl-maleimide (NEM) on Δ5-and Δ6-desaturase activities and the incorporation of substrates and products into different microsomal lipid classes and phospholipid (PL) subclasses were studied in human fetal liver microsomes, obtained after legally approved therapeutic abortion. Desaturase activities were measured by a radiochemical method using reversed-phase high-performance liquid chromatography (HPLC). After nonphospholipid (NPL) and PL separation on silica cartridges, the radioactivity in different lipids of the NPL group was assessed by two-dimensional thin-layer chromatography, and their fatty acid (FA) composition by gas-liquid chromatography. The PL subclasses were separated, and the distribution of radioactivity between products and substrates was determined in PL subclasses. NEM inhibited the Δ5- and Δ6-desaturase activities in the n−6 series of FA but not the Δ6-desaturase activity in the n−3 series, which suggests the existence of two distinct Δ6-desaturases, one for the n−6 series and another for the n−3 series. Whether NEM was present or absent, most of the radioactivity was recovered in the free FA form (about 80%). The desaturation products, obtained in the presence or absence of NEM, were preferentially incorporated into PL, suggesting a channeling of the newly synthesized FA toward microsomal PL. The comparison of the distribution of substrates and products incorporated into the different PL classes showed that most of the labeled FA were incorporated into phosphatidylcholine and to a lesser degree into phosphatidylethanolamine.     

Effect of n−3 fatty acid deficiency on fatty acid composition and metabolism of aminophospholipids in rat brain synaptosomes

Docosahexaenoic acid (DHA, 22∶6n−3) is one of the major polyunsaturated fatty acids esterified predominantly in aminophospholipids such as ethanolamine glycerophospholipid (EtnGpl) and serine glycerophospholipid (SerGpl) in the brain. Synaptosomes prepared from rats fed an n−3 fatty acid-deficient safflower oil (Saf) diet had significantly decreased 22∶6n−3 content with a compensatory increased 22∶5n−6 content when compared with rats fed an n−3 fatty acid-sufficient perilla oil (Per) diet. When the Saf group was shifted to a diet supplemented with safflower oil plus 22∶6n−3 (Saf+DHA) after weaning, 22∶6n−3 content was found to be restored to the level of the Per group. The uptake of [³H]ethanolamine and its conversion to [³H]EtnGpl did not differ significantly among the three dietary groups, whereas the formation of [³H]lysoEtnGpl from [³H]ethanolamine was significantly lower in the Saf group than in the other groups. The uptake of [³H]serine, its incorporation into [³H]SerGpl, and the conversion into [³H]EtnGpl by decarboxylation of [³H]SerGpl did not differ among the three dietary groups. The observed decrease in lysoEtnGpl formation associated with a reduction of 22∶6n−3 content in rat brain synaptosomes by n−3 fatty acid deprivation may provide a clue to reveal biochemical bases for the dietary fatty acids-behavior link.     

Modulation of renal injury in pcy mice by dietary fat containing n−3 fatty acids depends on the level and type of fat

Low-fat diets and diets containing n−3 fatty acids (FA) slow the progression of renal injury in the male Han:Sprague-Dawley (SPRD)-cy rat model of polycystic kidney disease. To determine whether these dietary fat effects are similar in females and in another model of renal cystic disease, in this study we used both male and female pcy mice to examine the effects of fat level and type on disease progression. Adult pcy mice were fed 4, 10, or 20 g soybean oil/100 g diet for 130 d in study 1. In study 2, weanling pcy mice were fed high or low levels of fat rich in 18∶2n−6 (corn oil, CO) 18∶3n−3 (flaxseed oil/CO 4∶1 g/g, FO), or 22∶6n−3 (algal oil/CO 4∶1 g/g, DO) for 8 wk. In adult pcy mice, low-compared with high-fat diets lowered kidney weights (2.4±0.2 vs. 3.1±0.2 g/100 g body weight, P=0.006) and serum urea nitrogen (SUN) (9.6±0.6 vs. 11.9±0.6 mmol/L, P=0.009), whereas in young pcy mice it reduced renal fibrosis volumes (0.44±0.04 vs. 0.62±0.04 mL/kg body weight, P<0.0001). FO feeding in young pcy mice mitigated the detrimental effects of high fat on fibrosis while not altering kidney size, function, and oxidative damage when compared with the CO-fed mice. In contrast, DO-compared with CO-fed mice had higher kidney weights (2.64±0.07 vs. 2.24±0.08 g/100 g body weight, P=0.005), SUN (9.4±0.57 vs. 7.0±0.62 nmol/L, P<0.0001), and cyst volumes (7.9±0.28 vs. 6.2±0.30 mL/kg body weight, P<0.0001) and similar levels of oxidative damage and fibrosis. The FA compositions of the diets were reflected in the kidneys: 18∶2n−6, 18∶3n−3, and 22∶6n−3 were the highest in the CO, FO, and DO diets, respectively. Dietary effects on kidney disease progression were similar in males and females. A low-fat diet slows progression of renal injury in male and female pcy mice, consistent with findings in the male Han:SPRD-cy rat. Dietary fat type also influenced renal injury, with flaxseed oil diets rich in 18∶3n−3 slowing early fibrosis progression compared with diets rich in 18∶2n−6 or in 22∶6n−3.     

Different kinetic in incorporation and depletion of n−3 fatty acids in erythrocytes and leukocytes of mice

n−3 PUFA are well known for their anti-inflammatory effects. However, there has been only limited study on the kinetics of incorporation and depletion of n−3 PUFA in immune cells. In the present study we investigated the incorporation and depletion of n−3 PUFA in erythrocytes and leukocytes in mice during a 6-wk feeding period. Over the first 3-wk period (the incorporation period) the mice were fed a special diet with a high n−3/n−6 PUFA ratio. In the following 3-wk period (the depletion period) the mice were fed a standard chow diet. A linear incease of the concentration of EPA and DHA in erythrocyte membranes was observed during the incorporation period, whereas a stagnation was observed after the second week for leukocytes. The level of EPA did not fall to the background level after the depletion period, and the level of DHA was kept almost constant during the depletion period in the erythrocyte membranes. In leukocytes the concentration of both EPA and DHA decreased during the depletion period, but did not reach the background level after the 3-wk depletion. In conclusion, the kinetics of EPA and DHA in the different cells are different. The rate of incorporation is faster than that of depletion for n−3 PUFA. More n−3 PUFA can be incorporated into leukocytes in comparison with erythrocytes. The ratio of n−3/n−6 PUFA is more important than the amount of n−3 FA in changing the FA compositions of membrane lipids.     

Dietary n−3 polyunsaturated fatty acids increase T-lymphocyte phospholipid mass and acyl-CoA binding protein expression

Dietary flaxseed oil, which is enriched in α-linolenic acid, and fish oil, which is enriched inEPA and DHA, possess anti-inflammatory properties when compared with safflower oil, which is enriched in linoleic acid. The influence of flaxseed oil and fish oil feeding on lipid metabolism in T-lymphocytes is currently unknown. This study directly compared the effects of feeding safflower oil, flaxseed oil, and fish oil for 8 wk on splenic T-lymphocyte proliferation, phospholipid mass, and acyl-CoA binding protein expression in the rat. The data show that both flaxseed oil and fish oil increased acyl-CoA binding protein expression and phosphatidic acid mass in unstimulated T-lymphocytes when compared with safflower oil feeding. Fish oil feeding increased cardiolipin mass, whereas flaxseed oil had no effect. After stimulation, flaxseed oil and fish oil blunted T-lymphocyte interleukin-2 production and subsequent proliferation, which was associated with the lack of incraased acyl-CoA binding protein expression. The results reported show evidence for a novel mechanism by which dietary flaxseed oil and fish oil suppress T-lymphocyte proliferation via changes in acyl-CoA binding protein expression and phospholipid mass.     

Polyunsaturated n−3 fatty acids and the development of atopic disease

The relationship between polyunsaturated long-chain fatty acids and atopy has been discussed for decades. Higher levels of the essential fatty acids linoleic acid and α-linolenic acid and lower levels of their longer metabolites in plasma phospholipids of atopic as compared to nonatopic individuals have been reported by several, but not all, studies. Largely similar findings have been reported in studies of cell membranes from immunological cells from atopics and nonatopics despite differences in methodology, study groups, and definitions of atopy. An imbalance in the metabolism of the n−6 fatty acids, particularly arachidonic acid and dihomo-γ-linolenic acid, leading to an inappropriate synthesis of prostaglandin (PG) E₂ and PGE₁ was hypothesized early on but has not been corroborated. The fatty acid composition of human milk is dependent on the time of lactation not only during a breast meal but also the time of the day and the period of lactation. This explains the discrepancies in reported findings regarding the relationship between milk fatty acids and atopic disease in the mother. Prospective studies show disturbances in both the n−6 and n−3 fatty acid composition between milk from atopic and nonatopic mothers. Only the composition of long-chain polyunsaturated n−3 fatty acids was related to atopic development in the children, however. A relationship between lower levels of n−3 fatty acids, particularly eicosapentaenoic acid (20∶5 n−3), and early development of atopic disease is hypothesized.     

The electrophysiologic basis for the antiarrhythmic and anticonvulsant effects of n−3 polyunsaturated fatty acids: Heart and brain

The n?3 polyunsaturated fatty acids (PUFA) have been shown to be antiarrhythmic in animals and probably in humans. PUFA stabilize the electrical activity of isolated cardiac myocytes by modulating sarcolemmal ion channels, so that a stronger electrical stimulus is required to elicit an action potential and the refractory period is markedly prolonged. Inhibition of voltage-dependent sodium currents, which initiate action potentials in excitable tissues, and of the L-type calcium currents, which initiate release of sarcoplasmic calcium stores, thus increasing cytosolic free calcium concentrations and activating the contractile proteins in myocytes, appears at present to be the probable major antiarrhythmic mechanisms of PUFA. Because the ion channels in neurons have channel proteins essentially homologous to those in the heart, the n?3 fatty acids would appear to be likely to affect the electrical activity in the brain in a manner similar to their effects in the heart, and accumulating evidence supports this notion. Evidence of important beneficial neurological effects of dietary n?3 PUFA are emerging with more likely to be discovered.